Color image forming materials have come to prevail over black-and-white image forming materials. They have found wide applications, such as ink jet recording materials, thermal transfer recording materials, electrophotographic recording materials, transfer type silver halide photographic materials, printing inks, recording pens, and color filters in solid-state image sensors, such as charge coupled devices (CCDs), and in displays, such as liquid crystal displays (LCDs) and plasma display panels (PDPs).
These color image recording materials and color filters use colorants (dyes and pigments) of additive or subtractive primaries to implement full color reproduction or recording. Nevertheless, colorants having absorption characteristics suitable for favorable color reproduction and fastness against various conditions of use or environmental conditions are not available for the time being.
Ink jet recording has been popularized rapidly and will see further development because of low material cost, high speed, low noise, and ease of color recording. Fundamentally, ink jet recording is divided into a continuous method in which ink droplets are continuously allowed to fly and a drop-on-demand method in which ink droplets are made to fly upon image information signals. The mechanism of drop formation includes a piezoelectric system in which pressure is applied to ink by a piezoelectric element to eject ink droplets, a thermal system in which an air bubble is generated by heat to eject ink droplets, an acoustic system, and an electrostatic system in which ink droplets are sucked or ejected by an electrostatic force. Ink-jet inks include aqueous ink, oily ink, and solid ink (melting type).
Colorants used in ink-jet inks are required to have (1) good solubility or dispersibility in ink solvents, (2) capability of forming a high-density image, (3) satisfactory hues, (4) color fastness against light, heat, active gases in the environment (e.g., NOx, oxidizing gases such as ozone, SOx, etc.), (5) resistance against water or chemicals, (6) good fixability on media with minimized feathering, (7) stability in ink formulations, (8) nontoxicity, (9) high purity, and (10) inexpensiveness. It is extremely difficult to obtain colorants meeting all these requirements. It has been particularly desired to develop colorants which have a favorable magenta hue and are fast to light, humidity, heat, and oxidizing gases in the environment, such as ozone. Oxidizing gas resistance is of special concern where an image is formed on a medium having an ink-receptive layer containing porous white inorganic pigment particles.
Color copiers and color laser printers making use of an electrophotographic system usually employ color toners having a dye or a pigment as a colorant dispersed in a resin binder. Color toners are required to have absorption characteristics suitable for favorable color reproduction, high light transmission (transparency) particularly for use in an overhead projector (OHP), and color fastness against various environmental conditions of use. Toners comprising a pigment dispersed in particles are disclosed in JP-A-62-157051 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-62-255956, and JP-A-6-118715. While excellent in light-fastness, these toners, being insoluble, agglomerate easily, which can cause reduction in transparency or change in hue of transmitted light. Toners comprising a dye are disclosed in JP-A-3-276161, JP-A-7-209912, and JP-A-8-123085. Although they have high transparency and do not change in hue, there is a question as to light-fastness.
A thermal transfer recording system has advantages such as a small size which leads to cost reduction, ease of operation and maintenance, and a low running cost. Colorants used in thermal transfer recording are required to have absorption characteristics suitable for favorable color reproduction, balance between thermal transfer properties and post-transfer fixability, heat stability, and color fastness to various factors. None of known colorants satisfies all these requirements. For example, JP-A-60-2398 proposes a thermal transfer recording material and an image formation method in which a thermally diffusing colorant is chelated with a transition metal ion having been added to an image-receiving medium. However, the absorption characteristics of the formed chelated compound are unsatisfactory. Further, use of a transition metal is environmentally problematical.
Color filters, which are required to have high transparency, have been produced by dyeing with dyes. For example, a dyeable photoresist is imagewise exposed to light and developed to form a pattern for each color and successively dyed with the respective dyes to produce a color filter. Color filters are also produced by using a positive resist as taught in U.S. Pat. No. 4,808,510 and JP-A-6-35182. Color filters produced by using dyes exhibit excellent optical characteristics with high light transmission but have limited resistance to light and heat. Dyes having various resistance properties as well as high transparency have therefore been demanded. On the other hand, methods of producing color filters by using organic pigments resistant to light and heat instead of dyes are widely known but have difficulty in achieving such optical characteristics as with dyes.
The properties required, in common, of colorants used in the above applications are (1) absorption characteristics suitable for color reproduction, (2) color fastness against various environmental conditions of use, such as fastness to light, heat, humidity, oxidizing gases such as ozone, and chemicals such as sulfurous acid gas, and (3) a large molar absorptivity.
Coupling components that have been widely used for azo dyes include phenols, naphthols, and anilines. JP-A-11-209673 and Japanese Patent 3020660 disclose azo dyes obtained by using these coupling components, which have satisfactory hues but poor light fastness. Lately, Japanese Patent Application No. 2000-220649 proposed dyes with satisfactory hues and improved light fastness. However, all the colorants known by the literature are extremely unsatisfactory in fastness to oxidizing gases such as ozone.
In seeking for colorants with satisfactory resistance to oxidizing gases such as ozone, the present inventors have arrived at the idea of using a nitrogen-containing heterocyclic compound as a coupling component, dropping the idea of using the conventional coupling components such as phenols, naphthols, and anilines. Patent applications relevant to azo dyes comprising a pyridine coupling component or a pyrazine coupling component include JP-A-49-74718, EP23309, and DE 2513949, DE 2832020, and DE 2525505. At the time of filing these applications it was unknown that these dyes are applicable to image formation by ink jet recording and the like; moreover the azo dyes disclosed in these publications have insufficient fastness to light, heat, humidity, and active gases in the environment and also insufficient hues as magenta dyes.